UV LED array with power interconnect and heat sink

ABSTRACT

A heat sink and power interconnect for a UV LED array are provided. A first circuit is disposed on a surface of a first substrate. A UV LED array is positioned thereon. A second substrate and second circuit are spaced apart from the first substrate and a first heat sink is positioned adjacent thereto. An aperture passes through each of the first substrate, the second substrate, and the heat sink. An electrical insulator lines the aperture with an electrically and thermally conductive liner positioned adjacent to the electrical insulator. A fastener is positioned in the aperture and electrically interconnects the first circuit and the second circuit through the electrically and thermally conductive liner and electrically communicates with an external power supply. The fastener carries one or more of a power or an electrical signal, and dissipates heat through the electrically and thermally conductive liner to the heat sink.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from (1) U.S. Provisional PatentApplication Ser. No. 62/780,946 filed Dec. 18, 2018; and (2) U.S.Provisional Patent Application Ser. No. 62/832,286 filed Apr. 11, 2019,and the disclosures of which are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates to electrical connections in devicelayouts and, more particularly to electrical connections in high powerdevice layouts such as UV LED arrays.

BACKGROUND

Many electronic devices and electrical equipment use a variety ofwire-based connectors for communication with power supplies or withother electrical devices. However, as the footprint of these devicesbecomes smaller, there is a higher power density and wired connectionscan be difficult to establish and maintain. Further, high powerdensities may create high amounts of heat that can damage solderconnections holding wires. For example, conventional LEDs use variouswired connections between a power source and the LED module. However,this wire connection is a source of failure, particularly for solderconnections, terminals with wires, or connectors with wire connectionsthat may weaken due to thermal fatigue or mechanical strain. Wireconnections are also a source of defective products duringmanufacturing. In contrast to conventional lighting approaches, LEDlighting technologies have relatively high efficiency, which generatesless heat. However, the newly-developed UV LEDs generating some veryshort wavelengths below 400 nm typically have a relatively lowconversion efficacy, thus generating large amount of heat. In order toimprove the efficient and maintain a compact structure, a new design tointegrate the power path and heat dissipation functions is important. Asused herein, the term “UV” is broadly construed to relate to all formsof UV ration, including UV, UV-A, UV-B, UV-C near UV, etc. In general,the term “UV” will apply to wavelengths from approximately 10 nm toapproximately 440 nm.

In traditional techniques for UV applications, organic materials (e.g.electric cable insulation jackets, insulation materials of connectors,sockets or terminals) would normally be used as the connectingmaterials. However, UV light as well as the heat will cause degradationunder the long-term exposure of the short wavelength illumination,therefore, new designs are needed that improve heat dissipation whilefacilitating compact design.

Current UV arrays may employ ceramic substrates, to reduce thermaleffect, but there are drilled holes for connection if connectors areused. Too much heat may generate the risks of cracking on the locationsof connectors.

Further, when LEDs are used in large arrays, considerable heat isgenerated due to the high power density concentrated in a small area.This heat, particularly the extreme thermal cycling as the devices areheated and cooled, may damage conventional connections. Additionally,unstable connections may fail such as those due to poor soldering ormisalignment of wires and solder.

LED arrays also generate substantial amounts of light. In some cases,the amount of light generated may be two orders of magnitude greaterthan full sunlight in the middle of the day. This amount of light mayalso damage soldered wire connections, causing power failures in LEDarrays.

Therefore, there is a need in the art to have improved electricalconnections between LEDs and power sources.

Further, there is a need for improved interconnect structures for othersystems currently connected by wires. That is, an improved interconnectstructure has numerous applications beyond LEDs and LED arrays.

There is a further need to improve efficiency and maintain compactdevice structures, and, in particular, a need for a new design tointegrate a power path with heat dissipation functions.

SUMMARY OF THE INVENTION

The present invention provides a heat sink and power interconnect for aUV LED array. A first substrate is selected from a printed circuitboard, ceramics, or glass-ceramics material. A first circuit is disposedon a surface of the first substrate. A UV LED array is positioned on aportion of the first circuit or on the surface of the first substrate,the UV LED electrically communicating with the first circuit.

A second substrate is spaced apart from the first substrate with asecond circuit disposed on a surface of the second substrate. At least afirst heat sink that is configured to dissipate heat from the UV LEDarray is positioned adjacent to at least one or both of the firstsubstrate and the second substrate. An aperture passes through each ofthe first substrate, the second substrate, and the heat sink. Anelectrical insulator lines the aperture with an electrically andthermally conductive liner positioned adjacent to the electricalinsulator.

An electrically- and thermally-conductive fastener is positioned in theaperture and contacting the electrically- and thermally-conductive linersuch that the fastener electrically interconnects the first circuit andthe second circuit through the electrically and thermally conductiveliner and electrically communicates with an external power supply,carrying one or more of power or an electrical signal, and dissipatesheat through the electrically and thermally conductive liner to the atleast first heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a fastener interconnect according to anembodiment of the present invention.

FIG. 2 schematically depicts a fastener interconnect according to afurther embodiment of the present invention;

FIG. 3A-3F schematically depict a UV LED array with a fastenerinterconnect according to an embodiment of the present invention;

FIG. 4 schematically depicts a UV LED array with fastener interconnectaccording to a further embodiment of the present invention.

FIG. 5 schematically depicts a thermocouple probe with fastenerinterconnect according to an embodiment of the present invention;

FIG. 6 schematically depicts details of an actively-cooled heat sinkwith fastener interconnects according to an embodiment of the presentinvention;

FIG. 7A schematically depicts a cross-sectional view of a thin-filmheater with fastener interconnect according to an embodiment of thepresent invention;

FIG. 7B schematically depicts a perspective view of a thin-film heateraccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Turning to the drawings in detail, FIG. 1 depicts an overview of aconductive fastener assembly that overcomes the shortcomings ofconventional wiring. The conductive fastener is mechanically robust andeasily assembled with circuit boards and other substrate materials. Asdiscussed in further detail below, the fastener may interconnect betweena circuit that connects to an LED (or other devices that needs tocommunicate with a power supply) and other circuits that may bepositioned on another surface of the circuit board or substrate or bepositioned on another substrate.

In the example of FIG. 1, a first substrate 10 may be selected fromprinted circuit boards such as FR-X (PCB) or CEM-X (PCB) or may be aceramic such as aluminum nitride, silicon carbide, or alumina/sapphire.Other non-electrically-conductive substrates may also be selected suchas certain polymers, glass-ceramics, or metals with insulating ceramicor polymer layers positioned thereon. A conductive material 20 ispositioned on substrate 10 and may be patterned into a first electricalcircuit. A second substrate 30 is positioned apart from the firstsubstrate 10. Like substrate 10, substrate 30 may be selected fromprinted circuit boards, ceramic, or other non-conductive materials. Afurther conductive layer 40 is positioned on second substrate 30 and maybe patterned into a second electrical circuit. The conductive layers maybe copper, gold, silver, or alloys thereof or any other material withsufficient conductivity to carry electrical signals or power to a devicepositioned on the substrates or the conductive layers.

In FIG. 1, substrates 10 and 30 are positioned on either side of athermally conductive material core/heat sink 50. Typically, the core isselected from a metal core such as aluminum alloy, aluminum, copper,copper alloy, or stainless steel, however other conductive materials,including non-metals, may be used. Although the substrates arepositioned on either side of the conductive material core/heat sink,other configurations are also acceptable including those where one orboth substrates do not directly contact the heat sink or contact theheat sink through one or more intermediate layers.

An aperture 60 passes through the first and second substrates 10, 30,the first and second conductive layers 20, 40, and the heat sink 50. Anelectrical insulator 65 lines the aperture with an electrically andthermally conductive liner 70 positioned adjacent to the electricalinsulator. The electrical insulator 65 may be a ceramic or polymerinsulator although other insulating materials may also be used. Theelectrically and thermally conductive liner may be a metal such ascopper, copper alloys, aluminum, aluminum alloys, nickel, steel orconductive non-metals.

An electrically- and thermally-conductive fastener 80 is positioned inthe aperture 60 where it contacts the electrically- andthermally-conductive liner 70 such that the fastener 80 electricallyinterconnects the first circuit (conductor 20) and the second circuit(conductor 40) through the electrically and thermally conductive liner70. The fastener 80 may be, for example, a threaded fastener such as ascrew or bolt, or it may be an unthreaded fastener.

As seen in FIG. 2, additional circuits and heat sinks may also beinterconnected for more complex multilayer structures. In FIG. 2, theelectrically- and thermally-conductive liner 70 extends through a secondaperture 160 that passes through a second heat sink 160 and third andfourth substrates, 110 and 130, respectively. These third and fourthsubstrates include third and fourth conductive layers (optionallypatterned into circuits), elements 120 and 140, respectively in FIG. 2.Although not shown in FIG. 2, it is understood that further substratesand circuits, with or without additional heat sinks, may beinterconnected through the electrically- and thermally-conductive linerand fasteners 80, 180.

In the embodiment of FIG. 2, the circuit boards are separated by heatsinks and also air.

However, another heat sink may be located between boards 30 and 110.Other objects (e.g., additional substrate material) nay be used tomaintain or fix all structures in a stable state physically. Note thateach substrate may include more than one circuit. The quantity offasteners is selected based on the circuits interconnecting on thesubstrates. For existing high power-consumption electronic devices,there are numerous wires which contain signals or current and thosewires increase the system complexity, make maintenance or repair of thesystem difficult, and are sources of potential system failure. The, theconductive fastener interconnect system improves reliability. Thefastener 80 may be a unitary/integrated structure with a head and shankor the head and shank may be separable as shown with head 84 and shank82. Head 84 may be a nut that can engage one or more shanks as depictedin the interconnection of the two structures in FIG. 2. Note that,although not depicted, the use of the shank alone without a head portionmay be desirable in some circuit configurations. That is, the use of theterm “fastener” is in a broad sense of any element that can connectparts and does not denote a particular structure. The fastener functionsas a mechanical, electrical, and thermal connector. When using atwo-part fastener, the installation of the fastener may be differentthan for a one-part fastener, that is, the shank portion 82 may beinserted into an aperture and then the head be attached. A single headmay interconnect with multiple shanks which may be separately assembledand then joined together with the head.

The fasteners and electrically- and thermally conductive liner 70electrically communicate with an external power supply 200. The liner 70carries one or more of power or an electrical signal, and dissipatesheat through the electrically and thermally conductive liner to thefirst heat sink 50 (and, in FIG. 2, to second heat sink 150).

FIGS. 3A-3F depict the system of FIG. 1 employed in a UV LED array 300according to an aspect of the present invention. UV LED array 300includes a plurality of UV LEDs 310 arranged in rows (although otherarrangements may also be used) on a substrate 330. A circuit 320 ispositioned on a substrate 330. Depending upon the type of UV LEDs, theLEDs 310 are positioned on the substrate 330 or on the circuit 320 orpartially on the circuit and partially on the substrate 330. In FIG. 3A,a glass cover 340 is optionally positioned over the UV LEDs 310. Abovethe glass cover is positioned an optional lens or array of lenses ordiffuser elements 350.

As seen in FIGS. 3A, 3D, and 3F, apertures 370 are provided throughsubstrates 330. As seen in these FIGS., the conductive circuit 320contacts the conductive fastener 380 which then conducts power orsignals through conductive liner 365.

FIG. 4 depicts an aspect of a UV LED array 400 using “flip chip” bondingto further eliminate wire bond connections. The UV LEDs 410 includebonding pads 415 that connect to circuits 420 disposed on substrate 430.

The UV LED array with the conductive fastener system may be used in avariety of UV lithography apparatuses, such as those depicted in U.S.Pat. No. 9,128,387 and US Patent Application 2010/0283978, thedisclosures of which are incorporated by reference herein.Alternatively, the UV LED arrays of FIGS. 3 and 4 may be used in UVcuring systems and UV medical devices. Basically, the UV LED arrayincorporating the inventive conductive fastener interconnect system canbe used in any device requiring a UV source, and particularly useful fordevices that require a high-intensity UV source.

The flexibility of the present invention provides excellent reliabilityperformance, which is especially suitable for high power densityapplications (for example, greater than 30 watts/cm² in some embodimentsand greater than 60 watts/cm²) in other embodiments. It is also suitablefor working-area-dependent applications for UV LED arrays such as UVcuring, offset printing, UV sources for lithography, or thin-film heatgenerators. The configuration of the connection permits advanced thermalmanagement techniques to be employed including cooling tubes for gas orwater which may optionally be embedded in the thermal conductivitylayer. Further, the conductive fastener connection system may be usedwith irregularly-shaped substrates and circuit patterns.

The LED interconnect system is used in a variety of LED applicationssuch as lighting. In particular, the system is useful for LED-arraybased lighting such as for tubes used to replace conventionalfluorescent light bulbs, and other lighting that is designed to replaceincandescent lights. In general, all lighting applications thatcurrently use wires to supply power to the LED can substitute theconductive fastener and conductive tube structures to power individualLEDs or LED arrays.

In summary, the interconnect system of the present invention may be usedwith (i) high current, high power consumption applications (for example,from 1 amp to approximately 20-30 A) and with (ii) small working areathat results in high energy density and power density (can be used up tothe thermal limit of selected substrate or sub mount of apower-consuming device); (iii) the conductive fasteners are used as aconnection interface, with the performance and reliability beingsuperior to traditional soldering or connectors or terminals methods.

FIG. 5 depicts another application of the interconnect system of thepresent invention. FIG. 5 depicts a high-thermal-energy generatingdevice 500, such as an array of UV LEDs 510 (although any otherhigh-thermal-energy generating device may be used). The device 500includes a conductive circuit layer 520 and a substrate layer 530. Anoptional heat sink layer 550 may also be included. In one aspect, athermocouple 590 associated with a fastener 580, insulator 570 andthermally- and electrically-conducting liner 560 senses temperaturesbeneath substrate 530 while other thermocouples may sense temperatureson the surface of substrate 530.

FIG. 6 depicts an embodiment of the present invention using anactively-cooled heat sink. FIG. 6 depicts a high-thermal-energygenerating device 600, such as an array of UV LEDs 610 (although anyother high-thermal-energy generating device may be used). A substrate630 is positioned adjacent an actively-cooled heat sink 650. Thefastener interconnect system of fastener 680, insulating sleeve 670 andelectrically- and thermally-conducting liner 660 is positioned in anaperture that passes through the substrate 630 and the heat sink 650.Active cooling conduits 655 are positioned in the heat sink 650 and maycarry cooling fluid such as cooling gas or cooling liquid through theheat sink 650. In this manner, a greater amount of heat may bedissipated than for passively-cooled heat sinks. Note that theactively-cooled heat sink of FIG. 6 may be used with any of the otherembodiments of the present invention that employ a heat sink.

FIGS. 7A and 7B depict a thin-film heater 700 employing the interconnectsystem of the present invention. As seen in these FIGS., a resistanceheating thin film conductive layer 740 is disposed on substrate 730; thesubstrate may be an insulating substrate such as glass or ceramic orglass-ceramic material. The resistance heating layer may be anickel-chrome alloy (e.g., an alloy of approximately 80 percent nickeland 20 percent chrome) or any other resistive-heating material (e.g.,aluminum, aluminum alloys, indium tin oxide, tantalum nitride). Thefastener 780 passes through substrate 730 and into an aperture inelement 750; element 750 may be thermally-conductive and act as a heatsink. The aperture includes a sleeve of insulator 770 and electrically-and thermally-conductive liner 760.

In summary, the present invention has particular application with UVmodules/power modules for UV sources or arrays that have high currentlevels, for example, current of approximately 1 A-2 A up to a current ofapproximately 100 A. A particular current load capability is dependenton various criteria such as voltage, working area, fastener dimension,types of substrate materials, and the voltage/current relationship.Further, small working areas can use the fasteners of the presentinvention with space reduction over conventional wire bonds. Forexample, an LED module with dimensions of approximately 4×5 cm, 20 cm²,around 60-100 W with a 3-5 W/cm² (for an M3 screw size) electrical powerdensity are easily accommodated by the fastener systems of FIGS. 1 and2. It is understood that larger fasteners such as M5 and M10 screw sizesmay accommodate proportionately larger power densities.

Other applications for the conductive fastener interconnect systeminclude facilitating interconnection between batteries used, forexample, in electrical motor applications. Other applications include asinterconnections in modules in data centers (e.g., to interconnect racksin data centers). The interconnect system may also be used with otherhigh-power consumptions such as lasers or certain high-powersemiconductor devices. The broad applications for the present inventioncan eliminate many of wires, terminals or connectors in presentelectronic assemblies.

Advantages of the present invention include high reliability,particularly long-term reliability under the harsh conditions of highexposure to UV and repeated thermal cycling. It is also resistant tovibration and aging conditions. Since it eliminates various solderconnections, there is no wire classification and maintenance is simpleas the fasteners may be easily removed and replaced. The working area isalso improved as fasteners may be recessed from the device surface.Numerous other applications may incorporate the fastener interconnectsystem including power electronics, battery-to-battery connections,replacement of wires in rack systems, fan assemblies, etc.

Further, a lower amount of interface area can be achieved on the circuitsubstrates. Advantageously, heat dissipation would be limited at theinterface materials like glue, device soldering points, compared withthe prior art designs that have connectors or terminals or some wires.The use of the inventive fastener interconnection can reduce the risksof cracking because the surface area of the fastener is larger than theprior art connectors or other prior art interconnecting methods. Thus,the inventive fastener interconnection that reduces the interface isimportant to improve the heat dissipation issues and improve thereliability, extending the service life of the devices that use thefasteners.

The foregoing description of the present invention has been provided forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to the practitionerskilled in the art. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modificationsthat are suited to the particular use contemplated.

The invention claimed is:
 1. A heat sink and power interconnect for a UV LED array, comprising: a first substrate selected from an electrically insulating material or an electrically conductive material with one or more electrically-insulating layers positioned thereon, a first circuit disposed on a surface of the first substrate; a UV LED array positioned on a portion of the first circuit or on the surface of the first substrate; the UV LED array electrically communicating with the first circuit; a second substrate spaced apart from the first substrate; a second circuit disposed on a surface of the second substrate; at least a first heat sink configured to dissipate heat from the UV LED array; the heat sink positioned adjacent to at least one or both of the first substrate and the second substrate; an aperture passing through each of the first substrate, the second substrate, and the at least first heat sink; an electrical insulator lining the aperture; an electrically and thermally conductive liner positioned adjacent to the electrical insulator; a fastener positioned in the aperture and contacting the electrically and thermally conductive liner, the fastener electrically interconnecting the first circuit and the second circuit through the electrically and thermally conductive liner and electrically communicating with an external power supply, the fastener carrying one or more of power from the power supply or an electrical signal, and dissipating heat through the electrically and thermally conductive liner to the at least first heat sink.
 2. The heat sink and power interconnect for a UV LED array according to claim 1, wherein the heat sink is positioned adjacent to the first substrate and the second substrate such that the first substrate is positioned on a first surface of the heat sink and the second substrate is positioned on a second surface of the heat sink.
 3. The heat sink and power interconnect for a UV LED array according to claim 1, wherein the second substrate is spaced apart from the heat sink.
 4. The heat sink and power interconnect for a UV LED array according to claim 3, further comprising a second fastener cooperating with the second substrate.
 5. The heat sink and power interconnect for a UV LED array according to claim 4, further comprising a second heat sink positioned adjacent to the second substrate.
 6. The heat sink and power interconnect for a UV LED array according to claim 1, wherein the heat sink comprises one or metals selected from copper, aluminum, steel, stainless steel or alloys thereof.
 7. The heat sink and power interconnect for a UV LED array according to claim 1, wherein each of the first and second substrates are independently selected from ceramics, glass-ceramics, polymers, or metals coated with electrically-insulating layers.
 8. The heat sink and power interconnect for a UV LED array according to claim 1, wherein each of the first and second substrates are independently selected from printed circuit boards, alumina, silicon carbide, aluminum nitride, cordierite, or glass.
 9. The heat sink and power interconnect for a UV LED array according to claim 1, wherein either the electrical insulator or the electrically and thermally conductive liner is a tube positioned in the aperture.
 10. A combined interconnect and heat sink for high power devices, comprising: a first substrate selected from an electrically insulating material or an electrically conductive material with one or more electrically-insulating layers positioned thereon; a first circuit disposed on a surface of the first substrate; a high heat-generating device selected from a device that uses current of 1 amp or more or a device that generates heat of greater than approximately 30 Watts/cm², the high-heat generating device selected from one or more of a UV LED, a visible LED, a laser, or a thin film heater positioned on a portion of the first circuit or on the surface of the first substrate and electrically communicating with the first circuit; a second substrate selected from an electrically insulating material or an electrically conductive material with one or more electrically-insulating layers positioned thereon spaced apart from the first substrate; a second circuit disposed on a surface of the second substrate; a heat sink configured to dissipate heat from the high heat-generating device; the heat sink positioned adjacent to at least the first substrate or the second substrate; an aperture passing through each of the first substrate, the second substrate, and the heat sink; an electrical insulator lining the aperture; an electrically and thermally conductive liner positioned adjacent to the electrical insulator; a fastener positioned in the aperture and contacting the electrically and thermally conductive liner and wherein the fastener electrically interconnects the first circuit and the second circuit through the electrically and thermally conductive liner and electrically communicates with an external power supply, carrying one or more of power or an electrical signal, and dissipates heat through the electrically and thermally conductive liner to the heat sink.
 11. The combined interconnect and heat sink for high power devices according to claim 10, wherein the heat sink is positioned adjacent to the first substrate and the second substrate such that the first substrate is positioned on a first surface of the heat sink and the second substrate is positioned on a second surface of the heat sink.
 12. The combined interconnect and heat sink for high power devices according to claim 10, wherein the second substrate is spaced apart from the heat sink.
 13. The combined interconnect and heat sink for high power devices according to claim 10, further comprising a second fastener cooperating with the second substrate.
 14. The combined interconnect and heat sink for high power devices according to claim 12, further comprising a second heat sink positioned adjacent to the second substrate.
 15. The combined interconnect and heat sink for high power devices according to claim 10, wherein each of the first and second substrates are independently selected from ceramics, glass-ceramics, polymers, or metals coated with electrically-insulating layers.
 16. The combined interconnect and heat sink for high power devices according to claim 10, wherein the heat sink comprises one or metals selected from copper, aluminum, steel, stainless steel or alloys thereof.
 17. The combined interconnect and heat sink for high power devices according to claim 10, wherein each of the first and second substrates are independently selected from printed circuit boards, alumina, silicon carbide, aluminum nitride, cordierite, or glass.
 18. The combined interconnect and heat sink for high power devices according to claim 10, wherein either the electrical insulator or the electrically- and thermally conductive-liner is a tube positioned in the aperture. 